Investments (Summary Of The Cost And Carrying Value Of Trading Investments) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Investments [Line Items]
Cost	$ 114	$ 270
Carrying Value	124	267
Deferred Compensation Plan Mutual Fund Investments [Member]
Schedule of Investments [Line Items]
Cost	46	45
Carrying Value	53	46
Equity/Multi-Asset Class Mutual Funds [Member]
Schedule of Investments [Line Items]
Cost	62	174
Carrying Value	65	169
Foreign Debt [Member]
Schedule of Investments [Line Items]
Cost		12
Carrying Value		12
Corporate Debt [Member]
Schedule of Investments [Line Items]
Cost	6	39
Carrying Value	$ 6	$ 40